A gas turbine engine, typically used as a source of propulsion in aircraft, operates by drawing in ambient air, combusting that air with a fuel, and then forcing the exhaust from the combustion process out of the engine. A fan and compressor section, having low and high pressure compressors each with a plurality of blades rotating between a plurality of vanes, rotate to draw in and compress the ambient air. The compressed air then flows into the combustor, where it is split. A portion of the air is used to cool the combustor while the rest is mixed with a fuel and ignited.
Typically, an igniter generates an electrical spark to ignite the air-fuel mixture. The products of the combustion then travel out of the combustor as exhaust and through a turbine section. The turbine section, having high and low pressure turbines and a plurality of blades extending from each turbine, is forced to rotate as the exhaust expands through the turbine blades. The turbine section, fan, and compressor section are connected by concentrically mounted engine shafts running through the center of the engine. Thus, as the turbines rotate from the exhaust, not only is thrust created, but the fan and corresponding compressor rotate to bring in and compress new air. Once started, it can thereby be seen that the process is self-sustaining.
Combustors for gas turbine engines typically have a wall with a plurality of air holes, such as cooling or dilution holes, for admitting compressed air into the combustor. In an annular combustor, outer and inner walls cooperate to define, and are separated by, an annular combustion chamber. In most combustors, at least one igniter is also provided for igniting the air-fuel mixture extends through a wall of the combustor into the combustion chamber.
An annular combustor may further have a bulkhead, which may be segmented into panels in some combustor designs, at a forward end of the combustor and extending from the outer wall to the inner wall. At least one fuel nozzle extends through this bulkhead and into the combustion chamber to release the fuel. A swirler is generally positioned around each fuel injector to admit combustion air, create turbulence in the combustion air, and mix the combustion air and the fuel before the mixture is combusted.
Current combustor technology requires fuel nozzles which provide both a primary and a secondary flow of fuel to the combustor. Conventional fuel nozzles have a separate fitting, such as a b-nut, to attach each manifold, which provide the dual flow for these nozzles. While effective, these fittings are typically large, extend radially outward from the combustor, and require a large work tool access area in order to provide maintenance or to replace the fuel nozzles. Such large fittings and access areas increase the overall geometric envelope of the fuel nozzle and cause packaging difficulties for the engines.
When utilized in conjunction with aircraft, space and weight are at a premium and the engines must be as light and compact as possible. Therefore it can be seen that a fuel nozzle which can provide this dual flow of fuel to a combustor while requiring fewer parts and less space in the engine is needed.